This discussion is now closed.

Check out other Related discussions

Edexcel AS Chemistry module 2 revision thread.

Scroll to see replies

raam001584

so is it number of protons and electrons that affect size of van der waals? or just electrons

both sub-atomic particles are responsible for the temporary dipole to be set up in the molecule, so yes, both protons and electrons, although i'm sure you could get away with saying just electrons.

Reply 41

Mustard-man

Widowmaker

depends on whether you're using enthalpy of formation/enthalpy of combustion values

So for combustion are the 2 arrows always pointing down towards H2O and Co2. And for formation are the 2 arrows always pointing up from the elements?

thanks

Reply 42

Christophicus

gordon2002

So for combustion are the 2 arrows always pointing down towards H2O and Co2. And for formation are the 2 arrows always pointing up from the elements?

thanks

sounds good to me.

are you joking?

gordon2002

are you joking?

what do you mean? Yes that's correct.

Reply 45

Mustard-man

Oh right, I wasn't sure if it was. Thanks

Reply 46

hotboi01

hey, i have a question..why are iodoalkanes more reactive than choloalkanes and bromoalkanes

Reply 47

shimmerinapple

^yea. Can someone clarify that.

I need to request mark schemes for unit 2, June 01 and Jan 02. Anyone have them or know where i can get them?

Reply 48

snmichaels

hotboi01

hey, i have a question..why are iodoalkanes more reactive than choloalkanes and bromoalkanes

Factors Affecting Reactivity (or rate of hydrolysis):

1.) Polarity --> C-Cl os more polar than C-I, therefore a stronger attraction towards nucleophiles, one would expect a faster reaction.

2.) Bond Enthalpy --> decreases going down the group, C-I bond is most easily broken and should give faster reaction.

***Bond Enthalpy is the most dominant Factor***

You can shorten that depending on how many marks they want. If it were a 1 mark question, just mention the bond enthalpy being weaker down the group.

Reply 49

snmichaels

Not sure if these have been answered, but here goes...

ARCHK0VEN

One of the isomers of C4H8 reacts with HBR to give 2 different products, the major one of which is a chiral molecule.

i) Identify this isomer of C4H8
But-1-ene

ii) Give the mechanism for the reaction of this isomer with HBr
Electrophilic addition

iii)why is the major product Chiral, but the minor one not?
It is a molecule with with four different groups, about a central carbon atom (a chiral centre). I don't think stereoisomerism is in AS, not 100% sure though.

iv) Why is the chiral product the major one, and the non-chiral the minor one?
The chiral product is major becuase with an unsymmetrical alkene, the hydrogen from the hydrogen halide always adds to the carbon atom carrying more H-atoms. Hence, but-1-ene + HBr --> 2-Bromobutane, not 1-Bromobutane (the majority of the time).

v) The major product of this addition reaction is found to be optically inactive, explain why? :confused:

Reply 50

Gabrielle

state the reagent and conditions, and draw the products of the hydrolysis of transbutene

give the name of the reaction and product between the reactants:
- propanamine and KCN

has any1 answered these? i might have missed it - but i'm stuck.
i hate revising this module! (it may even be worse than statistics!)

Reply 51

Mustard-man

Gabrielle

well the reaction to get propanamine is to heat the halogenopropane in a dry sealed tube with NH3 + ethanol. This is a nucleophilic substitution giving the (alkane)amine. (NH2)

The other reaction is KCN + ethanol + halogenoalkane, heating under reflux. This gives an (alkane) nitrile (CN), again this is a nucleophilic substitution.